Slide-out mechanisms are used extensively in recreational vehicles, such as for storage trays, tank carriers and slide-out rooms. When slide-out mechanisms are used for slide-out rooms it is desirable to have such a room be flush with the floor of the main room from which the slide-out room extends. This has been done by allowing the slide-out room to move vertically during its operation such that the slide-out room is supported above the floor of the main room in its fully retracted position, and when it is fully extended it is lowered to the same plane as the floor of the main room. During this process a mechanism that actuates the sliding must compensate for the change in height as the slide-out room is operated. This has been particularly challenging when a rack and pinion mechanism is used to actuate a slide-out room since gear teeth used to engage a rack attached to a slide-out room tend to become disengaged as height of the slide-out room changes. There remains a need to have a slide-out mechanism which compensates for height changes and keeps gear teeth in contact with a mating rack at all times during operation.